This invention relates to catalytic hydrotreatment of a hydrocarbon feed comprising a whole shale oil or a shale oil fraction containing at least about 0.1 wt.% nitrogen.
In recent years increased concern over world crude oil supplies has focused considerable attention on converting low quality hydrocarbons to more useful products. Due to the relatively high levels of sulfur, nitrogen, and metals typically contained in such low quality hydrocarbons, hydrotreatment typically is required to upgrade such materials and thereby facilitate conversion to more valuable products.
Catalysts for hydrotreatment of hydrocarbon feeds are well known and, in general, comprise a hydrogenating component, typically a Group VI and/or VIII metal, metal oxide, and/or metal sulfide deposed on a support comprising a porous refractory inorganic oxide. Examples of useful commercial hydrotreating catalysts include cobalt-molybdenum deposed on silica, alumina, or silica-alumina, and nickel-molybdenum deposed on silica, alumina, or silica-alumina.
Incorporation of phosphorus into the hydrogenating component of various hydrotreatment catalysts has been proposed in the past. For example, Bertolacini et al., "Catalyst Development for Coal Liquefaction," Electric Power Research Institute Report AF-574, November, 1977, pp. 2-26 to 2-34, 3-23 to 3-27, Appendix B-1 to B-3 and Appendix C-3 to C-4, discuss on pp. 3-24 to 3-27 the use of phosphoric acid as an impregnation aid for the impregnation of metals on catalyst. On pp. 3-25 and 3-27, the discussion involves comparison of data for catalysts containing cobalt and molybdenum components deposited on an alumina support and for catalysts containing a phosphorus component as well as the cobalt and molybdenum components deposited on an alumina support. This discussion concludes on p. 3-27 with the following statement: "No advantage in desulfuriziation of a residual oil and other product qualities was found for the catalysts containing phosphorus." Furthermore, the report states on p. 3-29, with regard to the effect of phosphoric acid on the impregnation of both high and low surface area aluminas, that there appears to be no significant effect on product nitrogen content for either high or low surface area aluminas as a result of the use of phosphoric acid.
Recently, U.S. Pat. No. 4,224,144 (Hensley et al.) has disclosed hydrotreatment of shale oil and similar feeds using catalysts comprising a chromium component, a molybdenum component, and at least one Group VIII metal component deposed on a porous refractory inorganic oxide support. Such catalysts are prepared by sequential or single-step impregnation of a support with compounds of the metals and calcination of the result. Column 4, lines 37-59. According to the patentee, such catalysts exhibit improved denitrogenation and desulfurization activity as well as improved maintenance of such activity as compared to typical, commercial cobalt-molybdenum catalysts.
Despite the favorable results attained in accordance with Hensley et al., it can be appreciated that further improvements would be desirable, particularly in view of the decreasing supply of high quality feeds and attendant emphasis on maximizing yields of useful products from lower quality feeds. It is therefore an object of this invention to provide an improved process for denitrogenation of feeds containing relatively high levels of nitrogen. Other objects of the invention will be apparent to persons skilled in the art from the following description and the appended claims.
In contrast to the results disclosed in Hensley et al., Bertolacini et al. in the aforesaid EPRI Report AF-574, reported that the comparison in coal liquefaction studies of the use of a catalyst having cobalt, molybdenum, chromium and phosphorus components on an alumina support to the use of a catalyst having only cobalt, molybdenum and phosphorus components on an alumina support indicated only small improvements in desulfurization and denitrogenation as a result of the chromium component. The discussion of the benefits of the presence of chromia concludes on p. 2-34 of the EPRI Report with the following statement: "However, the differences relative to the chromia-free catalysts are of questionable significance." Thus, the benefits due to the presence of chromia in a catalyst containing cobalt, molybdenum and chromium components on alumina reported by Hensley et al. were not observed in the coal liquefaction studies of Bertolacini et al. when the catalyst additionally contained a phosphorus-containing component on the alumina.
Surprisingly, I have now found that the objects of this invention can be attained by incorporation of an effective amount of a phosphorus component into the hydrogenating component of hydrotreatment catalysts comprising a chromium component, a molybdenum component and at least one of a cobalt component and a nickel component, deposed on a support comprising at least one porous refractory inorganic oxide. Surprisingly, incorporation of a phosphorus component into the hydrogenating component according to this invention results in substantial improvements in denitrogenation performance as compared to catalysts that are similar but for incorporation of the phosphorus component. It also is surprising that the phosphorus component content can be adjusted to emphasize either denitrogenation activity or hydrogen consumption in that at relatively low concentration levels of the phosphorus component, unexpectedly high denitrogenation activity is attained at typical hydrogen consumption rates, whereas higher concentration levels of phosphorus component may give somewhat lower denitrogenation activity but with unexpectedly low hydrogen consumption. In addition, desulfurization activity of the invented catalysts is at least comparable to that of known catalysts containing a chromium component, a molybdenum component and at least one of a cobalt component and a nickel component.
Other proposals that may be of interest with respect to the present invention include those directed to improving the hydrotreatment performance of catalysts such as those of the aforesaid Hensley et al. patent, containing a hydrogenating component comprising a chromium component, a molybdenum component and at least one Group VIII metal component. Thus, workers in our laboratories have found that denitrogenation activity of catalysts containing such a hydrogenating component can be promoted by supporting the component on a silica-alumina containing about 10 to about 50 weight percent silica. It also has been found that catalysts comprising a porous refractory inorganic oxide, a crystalline molecular sieve zeolite and the aforesaid hydrogenating component exhibits improved denitrogenation and cracking activity. In both cases, improved denitrogenation activity has been attributed in part to increased acidity of the catalysts as compared to those of Hensley et al., although attempts by me and my co-workers to improve hydrotreatment performance by increasing acidity of catalysts containing a similar hydrogenating component through inclusion of other refractory inorganic oxides have proved unsuccessful. While not wishing to be bound by any particular theory or mechanism, it can be theorized that incorporation of phosphorus into the hyrogenating component of the invented catalysts serves to increase acidity and thereby promote denitrogenation activity. Even if that is the case, however, the use of silica-alumina supports or combinations of porous refractory inorganic oxides in combination with molecular sieve zeolites to increase acidity does not suggest incorporation of a phosphorus component into a hydrogenating component according to the present invention.